Posted
by
timothy
on Saturday December 19, 2015 @06:21AM
from the lucky-guess dept.

schwit1 writes: For the first time ever astronomers have been able to predict and photograph the appearance of a supernova, its light focused by the gravitational lensing caused by a galaxy and the dark matter that surrounds it: "The NASA/ESA Hubble Space Telescope has captured the image of the first-ever predicted supernova explosion. The reappearance of the Refsdal supernova was calculated from different models of the galaxy cluster whose immense gravity is warping the supernova's light." What makes this significant is that the prediction models were based on the theory of gravitational lensing and required the presence of dark matter to work. That they worked and were successful in predicting the appearance of this gravitationally bent light (bent by the dark matter it passed through) is a very strong confirmation of both concepts.

They didn't predict that a supernova was about to happen. They'd already seen the supernova happening in its ghost image created by gravitational lensing. They predicted where another image of the supernova would turn up.

It is a quite interesting thing being able to "re-watch" a Supernova from the beginning because the light has multiple paths towards Earth so we got a "warning" when it will happen.

The problem with a lot of Supernova explosions is that we often don't know what happened in the early phase (until it became bright enough to be noticed in wide-field pictures). It is most likely "a little bit" too far away to learn what type of star has exploded, but it still a great opportunity.

I'm just waiting for someone to pipe up that DM doesn't exist while not actually knowing what DM is. There are a few people who have valid opinions on it but almost all of the ones that I've noticed don't actually know what it is. (It's not really anything too specific yet, but we've got some ideas and some math. It's a placeholder.)

Nah, not all of us were bigots back then. Sure, many were but we were mostly just kids and being on base meant we were exposed to people from lots of cultures. Racism wasn't really that rampant where I was and by this time. It was elsewhere but I was kind of in an exclusion zone by virtue of living on or near base.

What I do find confusing is that I've seen, specifically, Polish jokes here on Slashdot that were moderated up. They're white so it's okay to be racist towards them? I've seen this happen on more than on occasion. One of them was, as I recall, +5 funny and I seem to recall 30% of the votes (if you click on 'em you can see 'em) were +1 informative.

Sadly, the joke that I'm mentioning wasn't even a good joke. It was just crude. Someone had said the screen door on a submarine joke and the follow up was, "Why do

I'm just waiting for someone to pipe up that DM doesn't exist while not actually knowing what DM is...(It's not really anything too specific yet, but we've got some ideas and some math. It's a placeholder.)

Since nobody knows what it is, anyone who says it doesn't exist would not know what it is.

Sort of true. I mean, yeah, it could turn out to be an effect caused by purple unicorn farts and it would still be dark matter.That's unlikely, and all, but it could happen. Something is causing this effect. Of course, some people seem inclined to not know the difference between dark energy and dark matter but that's a topic for another day.

I am not a physicist. I am a mathematician. I do find it fascinating but it's just a hobby.

We don't really know. The naming is unfortunate. It makes people come to all sorts of conflated confused conclusions - often without any help from others.;-) I liken it to calling it the God Particle. A very unfortunate naming process.

What DM is, and I'm just a layman, is what ever it is that causes this effect. Now, we've got some ideas and some maths and some of it even works. Proving this seems to be a bit of a stretch at this point but there are some folks thinking we might be able to really test it a

I realize you think you're being smart but, oddly enough, you're basically correct. Not only do *I* not know what it is, nobody else does either. They don't know how it works. They sure as hell have no idea how it exists. And, anyone who doesn't agree is *probably* an idiot. They may have a legitimate gripe but nobody has put forth a reasonable alternative.

See, it's basically what ever it is that is causing this effect that we see. We can see the effect. It seems like, with this news, we can even predict th

It is just a title to use, a placeholder, to describe the results we're seeing. It could be purple unicorn farts and it would still be dark matter. Though, I presume, they'll change the name if it turns out to be purple unicorn farts. I find the choice of title to be rather silly, it's like the "God Particle" all over again.

It is a quite interesting thing being able to "re-watch" a Supernova from the beginning because the light has multiple paths towards Earth so we got a "warning" when it will happen.

I though we were able to notice supernovas a short time in advance of when they occurred visually because neutrinos from the explosion make it out of the star well in advance of the other stuff. (So we see a few neutrinos and can tell the supernova is about to be visible).

Can someone confirm or deny? It's been a long time since I took astrophysics.

We can... in theory. The trouble is that our neutrino detectors aren't as sensitive as our optical telescopes. We can detect optical supernovae billions of light-years away, but we can only detect the neutrinos from a supernova within a few hundred thousand light-years.

The most recent supernova that was close enough to detect in neutrinos was in 1987 (SN1987A [wikipedia.org]). Three detectors spotted neutrinos from it a few hours before the optical supernova, but they only noticed this coincidence after the fact.

That's perfectly sensible. The cluster is five billion light-years from us, so the light from it has taken five billion years to reach us. The supernova is behind the cluster, at a distance of ten billion light-years, so it exploded ten billion years ago, and the light from it has taken ten billion years to reach us. (Five billion years to reach the cluster, and another five billion years to travel the rest of the way.)

You can do things in another reference frame, of course, and get different answers, bu

ESA Hubble Space Telescope has captured the image of the first-ever predicted supernova explosion.... What makes this significant is that the prediction models were based on the theory of gravitational lensing and required the presence of dark matter to work.

The important part here seems like confirmation of testable predictions made by Dark Matter theories. That's how science works: you have to make a falsifiable theory that makes testable predictions. Those predictions are then tested, to lend evidence toward or against the theories. This is key evidence in favor of Dark Matter.

I don't see how this supernova business relates at all to Dark Matter. The supernova happened in a galaxy already known to be gravitationally lensed by this other galaxy. Therefore it is predicted to show up in the gravitationally lensed image. The only involvement of Dark Matter is that, yes, we still need it for galaxy gravity to match our estimates of galaxy mass and gravitational strength. Just like it was needed to match galaxy rotation speed and non-supernova gravitational lensing. I mean, I suppose w

This tells us that the math is probably correct. I'm a layman but I'll try to explain. The resultant lensing is different than it would be if we did not know about DM. (We don't actually know what DM is, really.) We can observe the effects of DM. This is demonstrating that we're not getting the results we'd expect without DM but we're getting the results we expect *with* DM taken into account and, because of this, we were able to accurately predict where and when we'd be able to get a picture of it.

They were able to, according to NPR, detect it with something to do with minimal shifts in light with the moon and the theory is we're growing a beard of Dark Matter.

Yes, yes I phrased it just like that for you.:D Also, per your other comment, I'm betting it's Pink Unicorn Farts. What *is* interesting is that they were able to make some predictions and the maths worked out so that they were able to catch this on film. That's a da

Yeah, I can't find the NPR transcript either. (I know it was NPR 'cause that's all I listen to on the radio - it pisses the missus off but I've noticed she's listening.) And no, they're just detecting fluctuations and they appear to have found concentrations and our moon may impact them though they have no (observed) effect on the moon. That was how I understood it, at any rate. I'm still thinking it's unicorn farts. I bet I could wire up some math that looked good and checked out and attribute it to unicor

Nice! That's my thinking as well. This means, at least, that the maths that predict the results of Dark Matter are correct in this instance. This means that we're one step closer to, maybe, getting to figure it out a bit more. I read a bit of a study about some findings of "strands" (I think that's what they were calling them) that were quite close (around the moon) and that we're able to actually see, specifically, where the lensing is happening at it's greatest effect.

Dark matter has many testable predictions; armchair physicists who think they can second guess professionals only ever seem to know about rotation curves, and smugly decide that they know better.

Modified gravity only has the benefit of fitting certain observations - it has no theoretical backing. With most current data, modified gravity doesn't fit that well anyway. Its largely out of favour with physicists, only with those people who think that without any formal training in the subject they understand it

I wonder whether they could have used modified Newtonian dynamics to have made the same prediction.That is to say, I don't see how this prediction leans to either side in the dark matter vs MOND question.

It may not quite be "making shit up", but it certainly appears to be "ad hoc adjustment after the experiment to fit the result returned by the experiment". This isn't always invalid, but is certainly not very convincing. Theoretical tests need to predict the result before the experiment is run.

And another near brilliant observation on your part. That makes me strangely happy.;-) The last half dozen threads about Dark Matter had me feeling a bit disappointed with people. I love to learn new things and that's why I'm here.

At any rate, and correct me if I'm mistaken, that's why it is so important and impressive. This made a testable prediction and, yet again, we've determined that the math has been accurate enough to reasonably conclude that, well, the math is correct. This may, of course, imply mo

Hmm... I thought, and correct me if I'm wrong, that MOND was rather specifically meant to be used to deal with situational results that were unexpected or did not conform to the existing theories and maths? So, in other words, one area of the galaxy would use a slightly different model than another as there might be different effects seen in those areas.

An example would be that we'd find different areas of the galaxy with a greater concentration of dark matter than we'd find in other areas and thus, perhaps

Hmm... I thought, and correct me if I'm wrong, that MOND was rather specifically meant to be used to deal with situational results that were unexpected or did not conform to the existing theories and maths? So, in other words, one area of the galaxy would use a slightly different model than another as there might be different effects seen in those areas.

The intent of MOND, at least with most work, is to develop a universal law of gravity in the situation of low acceleration (or an alternative interpretation that affects all forces at low acceleration). This came about because early on fitting one galaxy rotation curve for the parameter, the acceleration scale where things become non-Newtonian, produced a result that work pretty well for other galaxies. As time went on though, more examples of other galaxies made this difficult, and there are couple diffe